The invention is related to an improved pad spring incorporated in a disk brake apparatus used to brake a vehicle such as an automobile. Specifically, the invention aims at realizing a structure which can stabilize the attitude of a pad while not in braking to effectively prevent occurrence of an abnormal noise called brake squeal.
In a disk brake apparatus used to brake a vehicle, a pair of pads are disposed to sandwich between them a rotor rotatable together with wheels and, in braking, the two pads are pressed against the two side surfaces of the rotor. The basic structure of such disk brake apparatus includes two kinds of structures of a floating type and an opposed piston type. FIGS. 8 to 12 show, of these two kinds of disk brake apparatuses, an example of the conventional structure of a floating caliper type of disk brake apparatus disclosed in the patent document 1.
Here, in the present specification and claims, “axial direction”, “circumferential direction” and “radial direction” mean the axial direction, circumferential direction and radial direction of the rotor unless otherwise stated. Further, “entrance side” means the side of the caliper where the rotor rotating together with the wheel enters the caliper, while “escape side” means the side where the rotor comes off from the caliper.
In the disk brake apparatus of the conventional structure, a caliper 3 is supported shiftably in the axial direction on a support 2 fixed to a vehicle body while it is opposed to the inner side surface of a rotor 1. Thus, on the circumferential-direction two end portions of (the inner side portions 6 to be discussed later) of the support 2, there are provided slide pins 4a, 4b while they project toward the inner side portions. The slide pins 4a, 4b are respectively engaged with a pair of support arm portions 5 projectingly formed in the circumferential-direction two sides of the caliper 3, thereby supporting the caliper 3 shiftably in the axial direction relative to the support 2.
The support 2 is constitutes of an inner side portion 6 disposed on the inner side of the rotor 1 and an outer side portion 7 on the outer side, while they are connected together in their respective circumferential-direction two ends by a pair of connecting arm portions 8a, 8b disposed to straddle over the rotor 1. To the circumferential-direction two ends of the inner side and outer side portions 6 and 7, there are fixed pad pins 9a, 9b, 10a and 10b while they extend in the axial direction. On the other hand, inner side and outer side pads 11a, 11 b are respectively constituted of linings 12, 12 and back plates 13, 13 attached to and supported by the backs of the linings 12, 12 and, in the circumferential-direction two ends of the back plates 13, 13, there are formed through holes 14a, 14b respectively. The pad pins 9a, 9b (10a, 10b) supported by the support 2 are loosely engaged into the respective through holes 14a, 14b. Using this structure, the two pads 11a, 11b are supported to be movable in the axial direction relative to the support 2.
The caliper 3 includes a cylinder portion 15 and a caliper pawl 16 while they sandwich the two pads 11a, 11b from the axial-direction two sides. The cylinder portion 15 incorporates therein a piston 17 for pressing the inner-side pad 11a toward the rotor 1.
To brake, pressure oil is fed into the cylinder portion 15 to allow the piston 17 to press the inner-side pad 11a against the inner side surface of the rotor 1. Then, as the reaction of this pressing force, the caliper 3 is shifted in the axial direction (toward the inner side), whereby the caliper pawl 16 presses the outer-side pad 11b against the outer side surface of the rotor 1. Thus, the rotor 1 is strongly held from both sides and is thereby braked.
In the disk brake apparatus of the above conventional structure, using the paired pad pins 9a, 9b, 10a, 10b respectively disposed in the axial direction, the two pads 11a, 11b are supported to be movable in the axial direction relative to the support 2. Thus, the shapes of the two pads 11a, 11b and support 2 can be formed symmetric with respect to their respective circumferential directions. This has an advantage in reducing the manufacturing cost of the disk brake apparatus.
However, in the disk brake apparatus of the above conventional structure, in braking, an abnormal sound called a clonk sound (click sound) is easy to occur. The reason for this is described with reference to FIG. 12.
When the rotation direction of the rotor 1 in the forward run of a vehicle is counterclockwise in FIG. 12, in braking, a brake tangential force F1 going toward the other side (in FIG. 12, the left side, escape side) in the circumferential direction is applied to the friction surface center A point of the lining 12 constituting the pad 11a. And, the pad 11a is slightly moved toward the other side in the circumferential direction, whereby the through hole 14a of the circumferential-direction one end portion (entrance side end portion) of the back plate 13 is engaged with the pad pin 9a fixed to the circumferential-direction one side portion of the support 2 to thereby support the brake tangential force F1 (that is, a so called pull anchor structure is established). Here, since the engagement portion between the through hole 14a and pad pin 9a is situated more inwardly in the radial direction than the action line of the brake tangential force F1, in the forward-run braking, to the pad 11a, there is applied the moment M1 based on the brake tangential force F1 to rotate the pad 11a counterclockwise.
On the other hand, in the vehicle backward-run braking, a brake tangential force F2 going toward the circumferential-direction one side (in FIG. 12, right side) is applied to the friction surface center A point. The pad 11a is slightly moved toward the circumferential-direction one side (entrance side) and the through hole 14b of the circumferential-direction other end portion of the back plate 13 is engaged with the pad pin 9b fixed to the circumferential-direction other end portion of the support 2 to thereby support the brake tangential force F2 (that is, a so called pull anchor structure is established). Here, since the engagement portion between the through hole 14b and pad pin 9b is situated more inwardly in the radial direction than the action line of the brake tangential force F2, in backward-run braking, to the pad 11a, there is applied the moment M2 based on the brake tangential force F2 to rotate the pad 11a clockwise.
Thus, in the disk brake apparatus of the conventional structure, the direction of the moment acting on the pad 11a (11b) in the forward-run braking and the direction of the moment acting on the pad 11a (11b) in the backward-run braking are opposite. Therefore, when the forward-run braking and backward-run braking are repeated, for example, in entering a vehicle into a garage in a parking lot, the pad 11a (11b) is caused to change its attitude greatly, specifically, it is rotated counterclockwise and clockwise. Therefore, the attitude of the pad 11a (11b) becomes unstable, whereby an abnormal sound called brake squeal is easy to occur and a clonk sound (click sound) is easy to occur.
Here, the above problem is not limited to the disk brake apparatus of a floating type but can occur similarly in a disk brake apparatus of an opposed piston type.
FIGS. 13 to 15 show an example of a disk brake apparatus according to the unpublished last invention that the inventors et al. have developed in view of the above circumstances. In the illustrated example, a pair of inner side and outer side pads 18a, 18b are incorporated in a disk brake apparatus 19 of an opposed piston type.
A caliper 20 constituting the disk brake apparatus 19 supports two pads 18a, 18b movably in the axial direction (the vertical direction of FIG. 13, the front and back directions of FIGS. 14, 15). The caliper 20 includes an inner body portion 21 and an outer body portion 22 disposed to hold the rotor 1 (see FIG. 10) between them, connecting portions 23a, 23b respectively for connecting together the end portions of the circumferential-direction one side (the right side of FIGS. 13 to 15, the entrance side in the vehicle forward run) of the inner and outer body portions 21, 22 and the end portions of the circumferential-direction other side (the left side of FIGS. 13 to 15, the escape side in the vehicle forward run), a central bridge portion 24 for connecting together the circumferential-direction central portions of the inner and out body portions 21, 22. A portion intervening between the circumferential-direction one end side connecting portion 23a and central bridge portion 24 and a portion intervening between the circumferential-direction other end side connecting portion 23b and central bridge portion 24 are respectively formed as window portions 30a, 30b respectively having a substantially rectangular shape in their plan views. Within each of the inner, outer body portions 21, 22, there are provided two inner cylinders and two outer cylinders. Within the inner cylinders and outer cylinders, there are oil tight mounted inner pistons and outer pistons to be movable in the axial direction. The caliper 20 is supported and fixed onto the vehicle body side (the knuckle of a suspension device) by a pair of mounting seats 25a, 25b provided in the inner body 21.
On the radial inner-end near sections of the circumferential-direction one-end near the inner body portion 21 and the outer body portion 22, there are supported and fixed (fixedly provided) a pair of pad pins 26a, 26b concentrically in the axial direction while their respective leading ends are projected from the axial-direction inside surfaces of the inner and outer bodies 21 and 22. Such portions of the pad pins 26a, 26b as project from the axial-direction inside surfaces of the inner body portion 21 and the outer body portion 22 are respectively formed in a cylindrical shape having a circular section. The pad pins 26a, 26b, in the forward run braking, are engaged with through holes 33 (to be discussed later) formed in the pads 18a, 18b to thereby support the brake tangential force F1 applied to the pads 18a, 18b. 
Such end face of the connecting portion 23a covering the radial outer portions of the pad pins 26a, 26b as is opposed to the central bridge portion 24 in the circumferential direction is formed as a flat-surface shaped torque receiving surface 27 (existing on a virtual plane perpendicular to the brake tangential force). The torque receiving surface 27, in the backward run braking, is contacted with torque transmission surfaces 36 (to be discussed later) formed in the pads 18a, 18b to thereby support the brake tangential force F2 applied to the pads 18a, 18b. 
On the other hand, the mutually opposed axial-direction inside surfaces of the circumferential-direction other-end near sections of the inner and outer body portions 21 and 22 respectively include a pair of guide walls 28 respectively raised in the axial direction and having a substantially fan-like shape in their front views. The guide walls 28 respectively include, in their radial middle portions, guide recess grooves 29 respectively opened in the axial-direction inside surface and circumferential-direction one side surface.
The pads 18a, 18b are respectively constituted of linings (friction members) 31, 31 and metal-made back plates (pressure plates) 32, 32 supporting the backs of the linings 31, 31. The shapes of the circumferential-direction two end portions of the pads 18a, 18b (lining 31 and back plate 32) are asymmetric (the shapes of such two portions as including the center axis of the rotor 1 and sandwiching a virtual plane passing through the pad friction center A are asymmetric) with respect to the circumferential direction. That is, in the circumferential-direction one-end portions (entrance side end portions) of the back plates 32, 32, there are formed raised portions 34 having the through holes 33 for insertion of the pad pins 26a, 26b, whereas in the circumferential-direction other end portions (escape side end portions) of the back plates 32, 32, there are not formed such raised portions nor through holes, but there are formed ear portions 35 to be engaged with the guide recess grooves 29.
Specifically, in the radial inner end portions of the circumferential-direction one-end portions of the back plates 32, 32, there are formed substantially rectangular plate-shaped raised portions 34 projected toward the circumferential-direction one side. In such areas of the substantially central portions of the raised portions 34 as exist more inward in the radial direction than the action line of the brake tangential force applied in braking, there are formed the through holes 33 respectively penetrating through them in the axial direction and having a section of a substantially rectangular shape. On the other hand, in the radial middle portions of the side edges of the circumferential-direction other end portions of the back plates 32, 32, there are formed the projection-shaped ear portions 35 projected toward the circumferential-direction other side and smaller in size than the raised portions 34. The radial inside surfaces of the ear portions 35, in braking (in forward-run braking and backward-run braking), are contacted with the radial inside surfaces of the guide recess grooves 29 to thereby support the moment (rotation force) applied to the pads 18a, 18b. Further, of the side edges of the back plates 32, 32 on the circumferential-direction one side, in such areas of the radial outer end portions as exist more outward in the radial direction than the action line of the brake tangential force applied in braking and are opposed in the circumferential direction to the torque receiving surface 27 of the end face of the connecting portion 23a, there are formed torque transmission surfaces 36 each having a projectingly curved shape.
In this example, in order to support the above-structured two pads 18a, 18b movably in the axial direction relative to the caliper 20, the pad pins 26a, 26b are loosely inserted into the through holes 33 of the circumferential-direction one-end portions of the back plates 32, 32 and the ear portions 35 of the circumferential-direction other end portions of the back plates 32, 32 are loosely inserted into the guide recess grooves 29. Also, in this state, the torque transmission surfaces 36 of the circumferential-direction one-end portions of the back plates 32, 32 are disposed opposed to the torque receiving surfaces 27 in the circumferential direction.
In the above-structured prior invention, in braking, to the pads 18a, 18b, there is generated the moment having the following direction. This is described below specifically with reference to FIGS. 15A and 15B.
In the forward-run braking, as shown in FIG. 15A, to the friction surface center (pad effective diameter determined by the diameter, position and the like of the piston) A point of the lining 31 constituting the pad 18a (18b), there is applied the brake tangential force F1 going toward the other side (the left side of FIGS. 15A and 15B, escape side) in the circumferential direction. And, the pad 18a (18b) is moved slightly toward the other side in the circumferential direction, whereby the through hole 33 of the circumferential-direction one end portion of the back plate 32 is engaged with the pad pin 26a of the circumferential-direction one end near portion of the caliper 20 to thereby support the brake tangential force F1 (a so called pull anchor structure is established). Therefore, in the forward-run braking, to the pad 18a (18b), there is applied the moment M1 going to rotate the pad 18a (18b) counterclockwise, that is, to press down the circumferential-direction other side portion inwardly in the radial direction.
Also, in the vehicle backward-run braking, as shown in FIG. 15B, to the friction surface center A point, in a direction opposed in the circumferential direction to the brake tangential force F1 applied in the forward run, there is applied a brake tangential force F2 going toward the circumferential-direction one side (the right side of FIGS. 15A and 15B, or escape side). And, the pad 18a (18b) is moved slightly toward the circumferential-direction one side, whereby such the torque transmission surface 36, of the side edge portion of the back plate 32 on the circumferential-direction one end side, as exists more outward in the radial direction than the action line of the brake tangential force F2, is contacted with the torque receiving surface 27 to thereby support the brake tangential force F2 (a so called push anchor structure is established). Therefore, in the backward-run braking, to the pad 18a (18b), there is applied the moment M2 having a direction (the same direction as the moment M1) to rotate the pad 18a (18b) counterclockwise, that is, to press down the circumferential-direction other side portion inwardly in the radial direction.
As described above, in the structure of the prior invention, the directions of the moment M1, M2 acting on the pads 18a, 18b in the forward-run braking and backward-run braking can be made to coincide with each other. Therefore, even when the forward-run braking and backward-run braking are repeated, for example, when putting a vehicle in the garage in a parking lot, the attitudes of the pads 18a, 18b can be maintained in a state where they are left rotated counterclockwise. This can eliminate the need to change the attitudes of the pads 18a, 18b, thereby being able to prevent the occurrence of brake squeal and a clonk sound.
However, the structure of the prior invention as is, while not in braking, the pads 18a, 18b are easy to shake to facilitate the occurrence of brake squeal. Thus, firstly, the inventors devised an idea to mount a pad spring 37 as shown in FIGS. 16A to 16D onto the disk brake apparatus 19.
The pad spring 37 is made of an elastic and corrosion-resistant metal plate such as a stainless steel plate, has a substantially Q-like shape in its front view, and includes a mounting portion 38 and a pair of push-up arm portions 39, 39. The mounting portion 38 has an inverted-U shape in its front view and includes a partially arc-shaped base section 40 with its radial inner part opened and a pair of flat plate sections 41, 41 respectively extended inwardly in the radial direction from the two ends of the base section 40. The distance (opening width) between the opposed inside surfaces of the flat plate sections 41, 41 is smaller than the outside diameter dimension of the pad pins 26a, 26b, while the radius of curvature of the inner circumferential surface of the base section 40 is equal to or slightly larger than ½ of the outside diameter dimension of the pad pins 26a, 26b. 
The push-up arm portions 39, 39 are respectively bent 90° from the radial inner ends of the flat plate sections 41, 41 in their mutually opposing directions (plate thickness direction) with respect to the circumferential direction, and are extended in the axial direction. The push-up arm portions 39, 39 include, in their leading ends, retaining sections 42, 42 rising outwardly in the radial direction.
The above-structured pad springs 37, 37, as shown in FIG. 17, while straddling over the pad pins 26a, 26b from outside in the radial direction (with the pad pins 26a, 26b inserted into the base portion 40), are disposed respectively between the inner body portion 21 and inner-side pad 18a and between the outer body portion 22 and outer-side pad 18b and are supported on the pad pins 26a, 26b, and are supported on the pad pins 26a, 26b respectively. In this state, the radial outside surfaces of the push-up arm portions 39, 39 extended inwardly in the axial direction from the mounting portion 38 are contacted with the radial inside surfaces of the raised portions 34, 34 of the back plates 32, 32 constituting the pads 18a, 18b, and the retaining sections 42, 42 are contacted with the axial-direction inside surfaces of the raised portions 34, 34 respectively.
The above-mounted pad springs 37, 37 elastically press the radial inside surfaces of the raised portions 34, 34 outwardly in the radial direction with taking the pad points 26a, 26b as a supporting point. Thus, while not in braking, the inner circumferential surfaces of the through holes 33 of the raised portions 34, 34 can be kept pressed elastically against the outer circumferential surfaces of the pad pins 26a, 26b. This can stabilize the attitudes of the pads 18a, 18b and thus can prevent the occurrence of brake squeal.
However, when the above-structured pad spring 37 is used, the assembling performance (operation efficiency) of the disk brake apparatus 19 can be inevitably degraded. That is, the pad springs 37, 37 cannot be mounted after the pad pins 26a, 26b are inserted into the through holes 33 of the pads 18a, 18b but must be mounted before insertion of the pad pins. This complicates the assembling operation of the disk brake apparatus 19 to degrade its assembling performance.
Also, since, in order to prevent the occurrence of rust in the torque transmission surface 36 and torque receiving surface 27 due to corrosion, highly corrosion-resistant members must be interposed between the surfaces 27, 36, it can be imagined that the pad springs 37, 37 should have such function additionally. However, since the pad springs 37, 37 are arranged at opposite positions to the surfaces 27, 36 with respect to the radial direction, it is difficult to provide the pad springs 37, 37 with such function additionally. Thus, in order to interpose a highly corrosion-resistant member between the surfaces 36 and 27, this member must be structured separately from the pad springs 37, 37, which increases the number of parts and thus the number of assembling steps and management man-hours.
Further, since the pad springs 37, 37, after mounted, cannot be confirmed visually from outside in the radial direction of the disk brake apparatus 19, an operation to check for forgetting of mounting is complicated.
[Patent document 1] JP-A-2006-520449